1. Field of the Invention
The present invention relates to a disk drive and to an inertial latch for a disk drive. More particularly, the present invention relates to a hard disk drive ("HDD") having an inertial latch crash stop assembly to prevent the head(s) from leaving a ramp load during a shock event.
2. Description of the Prior Art and Related Information
A typical hard disk drive includes a head disk assembly ("HDA") and a printed circuit board assembly ("PCBA"). The HDA includes at least one magnetic disk ("disk"), a spindle motor for rotating the disk, and a head stack assembly ("HSA") that includes one or more read/write heads, each with at least one transducer for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly ("HGA") that extends from the actuator assembly and biases the head toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement. A "rotary" or "swing-type" actuator assembly comprises a body portion that rotates on a pivot bearing cartridge between limited positions, a coil portion that extends from one side of the body portion to interact with one or more permanent magnets to form a voice coil motor, and an actuator arm that extends from an opposite side of the body portion to support the HGA.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a head attached to the gimbal. The load beam has a spring function that provides a "gram load" biasing force and a hinge function that permits the head to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that carries the head and transmits the gram load biasing force to the head to "load" the head against the disk. A rapidly spinning disk develops a laminar air flow above its surface that lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be "flying" over the disk when in this state.
Understandably, such drives may be relatively sensitive to shocks occasioned by mishandling, excessive vibrations, drops and other events causing a rapid acceleration of the disk drive. Indeed, should the head crash into a spinning disk because of a rotational shock, for example, debris may be generated which may lead to read or write errors or may result in hard disk drive failure.
In an effort to mitigate the effects of such shocks (e.g., rapid accelerations), a number of latches have been developed to latch the HSA and prevent the head(s) from contacting the disk(s). The operative mechanism of such latches may be mechanical, electromechanical or magnetic in nature. The first function of a latch is typically to limit the travel of the HSA both toward the inner diameter (hereafter "ID") and toward the outer diameter (hereafter "OD") of the disk. The second function typically discharged by such latches is to prevent the heads of the HSA from leaving the ramp load (if a ramp load is present) or a landing zone on the disk (if a landing zone is present around, for example, the ID of the disk) during shock events that might otherwise jolt the heads from the ramp or landing zone and onto the data-carrying portion of the disk during non-operative conditions of the drive. However, existing latches suffer from a number of disadvantages.
Electromechanical latches and magnetic latches, for example, generally suffer from an excessively complex structure, high cost and limited shock performance. Indeed, electromechanical and magnetic latches conventionally rely on a metallic tang or similar structure protruding from the overmolded voice coil portion of the HSA. Either a permanent magnet or an electromagnet is then typically used to attract the tang and to latch the HSA when the drive is not in operation. The use of electromagnets and/or permanent magnets increases the complexity and hence the manufacturing cost of the drive. Moreover, to ensure adequate shock protection, the latching force (the force with which the latch holds the HSA tang to the permanent or electro-magnet) must be sufficiently strong. In the case of a permanent magnet, however, a high magnitude latching force requires a correspondingly high de-latching force to free the HSA tang from the attractive force of the magnet. Such de-latching force is typically achieved by so-called "resonance de-latching", wherein alternating current is applied to the voice coil portion of the HSA to cause the HSA to vibrate at a particular resonant frequency to break free of the attractive force of the permanent magnet. The stronger the magnet, however, the greater the current is necessary to de-latch the HSA when the drive is called into active operation. In turn, such large
de-latching current requires a higher capacity current driver, again further increasing cost and complexity. The permanent magnets used in magnetic latches, moreover, are often composite magnets. It may be possible, over time, for the magnetic material of such composite magnets to become dislodged and damage the disk medium.
Mechanical latches, on the other hand, provide some relief from the constraints inherent in the use of electromechanical and magnetic latches. However, purely mechanical latches are not believed to be effective in handling shock events of great magnitude or to exhibit a response time that is sufficiently rapid to secure the actuator assembly during high intensity and/or longer duration shock events. Moreover, the complexity of such mechanical latches places further demands upon the manufacturing and assembly of the drive components.
For example, one such prior art latch is an inertial latch for a ramp load hard disk drive used in mobile computing applications which includes numerous plastic and stamped metal parts, as well as an inertia-increasing weight which all must be joined together to form the latch, further contributing to relatively high costs and complex assembly steps. The plastic parts form separately manufactured inner and outer crash stops attached to a hard disk drive base. Also, a plastic interposer is coupled to the hard disk drive base via a metal pin attached to the base and a corresponding bore in the interposer. An elongated metal boom, having the inertia-increasing weight attached at one end of the boom, is coupled to the inner crash stop via a metal pin protruding from the inner crash stop and a corresponding bore in the boom. The outer crash stop includes a magnet for "latching" the head stack assembly when the heads are "parked" on a ramp load. A metallic member on a coil portion of the head stack assembly functions to latch onto the magnet such that latching occurs. When the hard disk drive is subjected to a shock event, the interposer and the boom interact to prevent the heads from leaving the ramp load. A protrusion from the coil portion contacts the interposer to prevent the heads from leaving the ramp load. A metal member on the interposer interacts with the voice coil motor magnets to return the interposer to its initial position, i.e., the interposer's position prior to the shock event. While such an inertial is suitable for its intended purpose, the numerous plastic and stamped metal parts, as well as the inertia-increasing weight, must all be joined together to form the latch, which contributes to relatively high costs and complex assembly steps.